ASTM D6781-02(2014)

Standard Guide for Carbon Reactivation

ABSTRACT
This set of guidelines is offered to users of activated carbon to provide a better understanding of the reactivation process and some of the problems associated with sending carbon off-site or to a third party for thermal reactivation. It is not intended to serve as an operating procedure for those companies or persons that actually operate reactivation facilities. This is true because each reactivation facility is unique, using different types of furnaces, using various operating and performance requirements, and running spent activated carbons either in aggregate pools (combining different suppliers of carbon) or in custom segregated lots. Additionally, proprietary information for each facility relative to the particular equipment used cannot be addressed in a general set of guidelines. The equipment used for thermal reactivation process usually consists of rotary kilns, vertical tube furnaces, fluidized beds, or a multiple hearth furnace. All of these can be fired directly or indirectly. Auxiliary equipment to the furnace or kiln consists of feed screws, dewatering screws, direct feed bins, dust control equipment, product coolers, screening equipment, off-gas pollution abatement equipment, and tankage.
SCOPE
1.1 This set of guidelines is offered to users of activated carbon to provide a better understanding of the reactivation process and some of the problems associated with sending carbon off-site or to a third party for thermal reactivation. It is not intended to serve as an operating procedure for those companies or persons that actually operate reactivation facilities. This is true because each reactivation facility is unique, using different types of furnaces, using various operating and performance requirements, and running spent activated carbons either in aggregate pools (combining different suppliers of carbon) or in custom segregated lots. Additionally, proprietary information for each facility relative to the particular equipment used cannot be addressed in a general set of guidelines.  
1.2 This standard does not purport to address any environmental regulatory concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate practices for reactivation prior to use.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.

General Information

• Status: Historical
• Publication Date: 30-Jun-2014
• ICS: 71.060.10 - Chemical elements
• Technical Committee: D28 - Activated Carbon
• Drafting Committee: D28.02 - Liquid Phase Evaluation

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6781 − 02 (Reapproved 2014)
Standard Guide for
Carbon Reactivation
This standard is issued under the fixed designation D6781; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 reactivated carbon—spent activated carbon that has
gone through a thermal reactivation process.
1.1 This set of guidelines is offered to users of activated
carbon to provide a better understanding of the reactivation 3.1.2 spent activated carbon—activated carbon that has
process and some of the problems associated with sending seen service in some application, and that has some adsorbate
carbon off-site or to a third party for thermal reactivation. It is on the carbon.
not intended to serve as an operating procedure for those
3.1.3 virgin carbon—activated carbon produced from a raw
companies or persons that actually operate reactivation facili-
material carbon source that has never seen service.
ties. This is true because each reactivation facility is unique,
using different types of furnaces, using various operating and
4. Procedure
performance requirements, and running spent activated car-
4.1 Thermal Reactivation Process :
bonseitherinaggregatepools(combiningdifferentsuppliersof
4.1.1 In order to appreciate the parameters or properties of
carbon) or in custom segregated lots. Additionally, proprietary
the spent activated carbon that influence the success of the
information for each facility relative to the particular equip-
reactivation process, one must have a basic understanding of
ment used cannot be addressed in a general set of guidelines.
the reactivation process and the equipment used therein.
1.2 This standard does not purport to address any environ-
Basically, the equipment and process used for reactivation is
mental regulatory concerns associated with its use. It is the
similar, if not identical, to those same items used for activation
responsibility of the user of this standard to establish appro-
of coal, coconut, wood, or other chars, into activated carbon,
priate practices for reactivation prior to use.
post devolatilization and carbon fixation (which are necessary
1.3 This standard does not purport to address all of the
steps in virgin carbon manufacture).
safety concerns, if any, associated with its use. It is the
4.1.2 The equipment used for these types of processes
responsibility of the user of this standard to establish appro-
usually consists of rotary kilns, vertical tube furnaces, fluidized
priate safety and health practices and determine the applica-
beds, or a multiple hearth furnace. All of these can be fired
bility of regulatory requirements prior to use.
directly or indirectly. Auxiliary equipment to the furnace or
kiln consists of feed screws, dewatering screws, direct feed
2. Referenced Documents
bins, dust control equipment, product coolers, screening
2.1 ASTM Standards:
equipment, off-gas pollution abatement equipment, and tank-
D2652 Terminology Relating to Activated Carbon
age.
2.2 Other Standard:
4.1.3 The spent carbon can come from either liquid or gas
AWWA B605-99 Standard for Reactivation of Granular
phase service. Thus, the spent carbon will contain more or less
Activated Carbon
water (or other liquids) depending on its service—less for gas
phase service compared to liquid phase service. Additionally,
3. Terminology
the carbon could be fed to the furnace as a water slurry if
3.1 Definitions: received in a bulk load, or if the spent carbon was slurried out
of adsorbers. Gross dewatering of such a slurry is normally
done by gravity separation of the water from the carbon in an
This guide is under the jurisdiction of ASTM Committee D28 on Activated inclined dewatering screw.
Carbon and is the direct responsibility of Subcommittee D28.02 on Liquid Phase
4.1.4 Once the spent carbon is introduced into the reactiva-
Evaluation.
tion furnace, the carbon undergoes a three-step process.As the
Current edition approved July 1, 2014. Published September 2014. Originally
spent carbon progresses through the furnace and is heated up,
approved in 2002. Last previous edition approved in 2007 as D6781 – 02 (2007).
DOI: 10.1520/D6781-02R14.
the carbon first loses moisture and light volatiles; then the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
carbon loses heavier volatiles by a combination of
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
vaporization, steam stripping, and thermal cracking of heavies
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. into a pseudo-char which deposits in the pores of the carbon;
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6781 − 02 (2014)
and then, the char is removed from the pores by gasification sugar or other large size organic molecules washed off the
with steam. This three-step process normally relies on the spent carbon as possible before charging to the reactivation
carbon being heated from ambient temperature to a tempera-
furnace. Otherwise, the sugars will caramelize inside the pores
ture approaching 1010°C (1850°F), with a reactivated carbon during reactivation and lessen product quality and rate through
discharge temperature of 871 to 954°C (1600 to 1750°F) being
the furnace.
typical. The steam ratio used is normally 1:1, with the pounds
4.2.2.2 Similarly, carbon used for decaffeination of coffee
of steam added to the furnace equal to the discharge rate of
must also be thoroughly “sweetened off” before charging to the
reactivated carbon leaving the furnace. This ratio can be
reactivation furnace.
adjusted up or down depending on the relative quality of the
4.2.2.3 Carbonsthatarecontaminatedwithlargeamountsof
spent activated carbon and the relative reactivated carbon
inorganic salts, gangue, fused salts, calcium oxide, or water
quality being produced, with higher quality (for example,
hardnesssolidsbycontactwithprocesswatersorsolutionsalso
higher iodine numbers, higher carbon tetrachloride numbers,
make poor quality reactivated products. There may also be
etc.) and harder to reactivate carbons demanding more steam.
potential leaching problems from the reactivated product (for
Spent carbons that have seen light service or are easy to
example, accumulated aluminum from alkaline reactivated
reactivate will demand less steam.
carbon). They may also cause problems with furnace slagging,
4.2 Reactivation Guidelines:
and afterburner slag formation. (Slag is the formation of fused
4.2.1 The purpose of the reactivation process is to remove inorganic materials, that may result in large masses that may
the accumulated contaminants from the activated carbon pores
plug up the furnace or afterburner flow passages.) It is
without damaging the carbon backbone. As described above, suggested that a test reactivation be done on these carbons to
this is done by a combination of devolatilization, steam
determine if reactivation can be done economically.
stripping, thermal cracking, and gasification. Thus, anything
Additionally, the economics can be influenced by whether
that increases the severity of the operation in terms of spent
these carbons are run in a segregated, or pool, manner.
carbon loading (that is, the amount of contaminants to be
4.2.2.4 Carbons that are contaminated with silanes,
removed), the tendency of the contaminants to create char, the
siloxanes, or organosilicones may cause problems with furnace
presence of higher boiling materials, or refractory material
slagging, and afterburner slag formation. It is suggested that a
(that is, material inert to devolatilization or gasification) makes
test reactivation be done on these carbons to determine if
the reactivation process less effective, even unattractive, in
reactivation can be done economically. Additionally, the eco-
terms of yield, cost effectiveness, or product quality for reuse.
nomics can be influenced by whether these carbons are run in
Ideally, reactivation leads to optimally restoring the adsorptive
a segregated, or pool, manner.
properties of the granular activated carbo
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6781 − 02 (Reapproved 2007) D6781 − 02 (Reapproved 2014)
Standard Guide for
Carbon Reactivation
This standard is issued under the fixed designation D6781; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This set of guidelines is offered to users of activated carbon to provide a better understanding of the reactivation process
and some of the problems associated with sending carbon off-site or to a third party for thermal reactivation. It is not intended to
serve as an operating procedure for those companies or persons that actually operate reactivation facilities. This is true because
each reactivation facility is unique, using different types of furnaces, using various operating and performance requirements, and
running spent activated carbons either in aggregate pools (combining different suppliers of carbon) or in custom segregated lots.
Additionally, proprietary information for each facility relative to the particular equipment used cannot be addressed in a general
set of guidelines.
1.2 This standard does not purport to address any environmental regulatory concerns associated with its use. It is the
responsibility of the user of this standard to establish appropriate practices for reactivation prior to use.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
requirements prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D2652 Terminology Relating to Activated Carbon
2.2 Other Standard:
AWWA B605-99 Standard for Reactivation of Granular Activated Carbon
3. Terminology
3.1 Definitions:
3.1.1 reactivated carbon—spent activated carbon that has gone through a thermal reactivation process.
3.1.2 spent activated carbon—activated carbon that has seen service in some application, and that has some adsorbate on the
carbon.
3.1.3 virgin carbon—activated carbon produced from a raw material carbon source that has never seen service.
4. Procedure
4.1 Thermal Reactivation Process :
4.1.1 In order to appreciate the parameters or properties of the spent activated carbon that influence the success of the
reactivation process, one must have a basic understanding of the reactivation process and the equipment used therein. Basically,
the equipment and process used for reactivation is similar, if not identical, to those same items used for activation of coal, coconut,
wood, or other chars, into activated carbon, post devolatilization and carbon fixation (which are necessary steps in virgin carbon
manufacture).
4.1.2 The equipment used for these types of processes usually consists of rotary kilns, vertical tube furnaces, fluidized beds, or
a multiple hearth furnace. All of these can be fired directly or indirectly. Auxiliary equipment to the furnace or kiln consists of feed
screws, dewatering screws, direct feed bins, dust control equipment, product coolers, screening equipment, off-gas pollution
abatement equipment, and tankage.
This guide is under the jurisdiction of ASTM Committee D28 on Activated Carbon and is the direct responsibility of Subcommittee D28.02 on Liquid Phase Evaluation.
Current edition approved Oct. 1, 2007July 1, 2014. Published November 2007September 2014. Originally approved in 2002. Last previous edition approved in 20022007
as D6781 – 02.D6781 – 02 (2007). DOI: 10.1520/D6781-02R07.10.1520/D6781-02R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6781 − 02 (2014)
4.1.3 The spent carbon can come from either liquid or gas phase service. Thus, the spent carbon will contain more or less water
(or other liquids) depending on its service—less for gas phase service compared to liquid phase service. Additionally, the carbon
could be fed to the furnace as a water slurry if received in a bulk load, or if the spent carbon was slurried out of adsorbers. Gross
dewatering of such a slurry is normally done by gravity separation of the water from the carbon in an inclined dewatering screw.
4.1.4 Once the spent carbon is introduced into the reactivation furnace, the carbon undergoes a three-step process. As the spent
carbon progresses through the furnace and is heated up, the carbon first loses moisture and light volatiles; then the carbon loses
heavier volatiles by a combination of vaporization, steam stripping, and thermal cracking of heavies into a pseudo-char which
deposits in the pores of the carbon; and then, the char is removed from the pores by gasification with steam. This three-step process
normally relies on the carbon being heated from ambient temperature to a temperature approaching 1010°C (1850°F), with a
reactivated carbon discharge temperature of 871 to 954°C (1600 to 1750°F) being typical. The steam ratio used is normally 1:1,
with the pounds of steam added to the furnace equal to the discharge rate of reactivated carbon leaving the furnace. This ratio can
be adjusted up or down depending on the relative quality of the spent activated carbon and the relative reactivated carbon quality
being produced, with higher quality (for example, higher iodine numbers, higher carbon tetrachloride numbers, etc.) and harder
to reactivate carbons demanding more steam. Spent carbons that have seen light service or are easy to reactivate will demand less
steam.
4.2 Reactivation Guidelines:
4.2.1 The purpose of the reactivation process is to remove the accumulated contaminants from the activated carbon pores
without damaging the carbon backbone. As described above, this is done by a combination of devolatilization, steam stripping,
thermal cracking, and gasification. Thus, anything that increases the severity of the operation in terms of spent carbon loading (that
is, the amount of contaminants to be removed), the tendency of the contaminants to create char, the presence of higher boiling
materials, or refractory material (that is, material inert to devolatilization or gasification) makes the reactivation process less
effective, even unattractive, in terms of yield, cost effectiveness, or product quality for reuse. Ideally, reactivation leads to optimally
restoring the adsorptive properties of the granular activated carbon while maintaining the carbon’s physical properties (especially
mechanical strength, density, and particle size). These two requirements do conflict to some extent: for example, reactivation
conditions severe enough to optimize adsorption properties may result in unacceptable decreases in mechanical strength and
density at the same time. This means that an optimal balance has to be found between restoring adsorption properties and
maintaining physical properties. Additionally, any non-carbon material that is introduced with the spent carbon into the furnace,
for example, sand, ceramic or metallic bed support material, sludges, oils, etc., reduces the final product quality in terms of
adsorptive capacity.
4.2.2 With this in mind, the normal applications for carbon that cover a broad spectrum of applications and industries do not
present any restrictions to the use of reactivation services to achieve good yields and good product quality. These applications
include potable water dechlorination, taste and odor removal, underground tank remediations, standard wastewater treatment
applications, most fugitive emission control applications, most solvent recovery applications, and most chemical purification
applications. A good reference for reactivation of granular activated carbon used in the drinking water market is standard AWWA
B605-99. However, there are several applications that require special care in the use of reactivation services, or that may
...